Method of altering and preserving the surface properties of a polishing pad and specific applications therefor

ABSTRACT

The present invention is directed, in general, to an improved material and method of planarizing a surface on a semiconductor wafer and, more specifically, to a method of altering the properties of polymers, preferably thermoplastic foam polymers, used in polishing applications. The chemical and mechanical properties thermoplastic foam substrates can be transformed by inorganic, inorganic-organic, and or organic-organic grafting techniques, such that the polymer foam is endowed with new set of properties that more desirable and suitable for polishing.

CROSS-REFERENCE TO PROVISIONAL APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/250,299 entitled, “SUBSTRATE POLISHING DEVICE ANDMETHOD,” to Edward M. Yokley, filed on Nov. 29, 2000; U.S. ProvisionalApplication No. 60/295,315 entitled, “A METHOD OF ALTERING PROPERTIES OFA POLISHING PAD AND SPECIFIC APPLICATIONS THEREFOR,” to Yaw S. Obeng andEdward M. Yokley, filed on Jun. 1, 2001; and U.S. ProvisionalApplication No. 60/304,375 entitled, “A METHOD OF ALTERING PROPERTIES OFA THERMOPLASTIC FOAM POLISHING PAD AND SPECIFIC APPLICATIONS THEREFOR,”to Yaw S. Obeng and Edward M. Yokley, filed on Jul. 10, 2001, which arecommonly assigned with the present invention and incorporated herein byreference as if reproduced herein in its entirety.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention is directed to polishing pads used forcreating a smooth, ultra-flat surface on such items as glass,semiconductors, dielectric/metal composites, magnetic mass storage mediaand integrated circuits. More specifically, the present inventionrelates to grafting and preserving the grafted surface of polymers,preferably thermoplastic foam polymers, thereby transforming theirmechanical and chemical properties to create more suitable polishingpads therefrom.

BACKGROUND OF THE INVENTION

[0003] Chemical-mechanical polishing (CMP) is used extensively as aplanarizing technique in the manufacture of VLSI integrated circuits. Ithas potential for planarizing a variety of materials in IC processingbut is used most widely for planarizing metallizied layers andinterlevel dielectrics on semiconductor wafers, and for planarizingsubstrates for shallow trench isolation.

[0004] In trench isolation, for example, large areas of field oxide mustbe polished to produce a planar starting wafer. Integrated circuits thatoperate with low voltages, i.e., 5 volts or less, and with shallowjunctions, can be isolated effectively with relatively shallow trenches,i.e., less than a micron. In shallow trench isolation (STI) technology,the trench is backfilled with oxide and the wafer is planarized usingCMP. The result is a more planar structure than typically obtained usingLOCOS, and the deeper trench (as compared with LOCOS) provides superiorlatch up immunity. Also, by comparison with LOCOS, STI substrates have amuch reduced “birds' beak” effect and thus theoretically provide higherpacking density for circuit elements on the chips. The drawbacks in STItechnology to date relate mostly to the planarizing process. Achievingacceptable planarization across the full diameter of a wafer usingtraditional etching processes has been largely unsuccessful. By usingCMP, where the wafer is polished using a mechanical polishing wheel anda slurry of chemical etchant, unwanted oxide material is removed with ahigh degree of planarity.

[0005] Similarly, integrated circuit fabrication on semiconductor wafersrequire the formation of precisely controlled apertures, such as contactopenings or “vias,” that are subsequently filled and interconnected tocreate components and very large scale integration (VLSI) or ultra largescale integration (ULSI) circuits. Equally well known is that thepatterns defining such openings are typically created by opticallithographic processes that require precise alignment with prior levelsto accurately contact the active devices located in those prior levels.In multilevel metallization processes, each level in the multilevelstructure contributes to irregular topography. In three or four levelmetal processes, the topography can be especially severe and complex.The expedient of planarizing the interlevel dielectric layers, as theprocess proceeds, is now favored in many state of the art IC processes.Planarity in the metal layers is a common objective, and is promoted byusing plug interlevel connections. A preferred approach to plugformation is to blanket deposit a thick metal layer on the interleveldielectric and into the interlevel windows, and then remove the excessusing CMP. In a typical case, CMP is used for polishing an oxide, suchas SiO₂, Ta₂O₅, W₂O₅. It can also be used to polish nitrides such asSi₃N₄, TaN, TiN, and conductor materials used for interlevel plugs, suchas W, Ti, TiN.

[0006] CMP generally consists of the controlled wearing of a roughsurface to produce a smooth specular finished surface. This is commonlyaccomplished by rubbing a pad against the surface of the article, orworkpiece, to be polished in a repetitive, regular motion while a slurrycontaining a suspension of fine particles is present at the interfacebetween the polishing pad and the workpiece. Commonly employed pads aremade from felted or woven natural fibers such as wool,urethane-impregnated felted polyester or various types of filledpolyurethane plastic.

[0007] A CMP pad ideally is flat, uniform across its entire surface,resistant to the chemical nature of the slurry and have the rightcombination of stiffness and compressibility to minimize effects likedishing and erosion. In particular, there is a direct correlationbetween lowering Von Mises stress distributions in the pad and improvingpolishing pad removal rates and uniformity. In turn, Von Mises stressesmay be reduced though the controlled production of pad materials ofuniform constitution, as governed by the chemical-mechanical propertiesof the pad material.

[0008] CMP pad performance optimization has traditionally involved theempirical selection of materials and use of macro fabricationtechnologies. For example, a pad possessing preexisting desirableporosity or surface texture properties may be able to absorb particulatematter such as silica or other abrasive materials. Or, patterns of flowchannels cut into the surface of polishing pads may improve slurry flowacross the workpiece surface. The reduction in the contact surface areaeffected by patterning also provides higher contact pressures duringpolishing, further enhancing the polishing rate.

[0009] Alternatively, intrinsic microtextures may be introduced intopads by using composite or multilayer materials possessing favorablesurface textures as byproduct of their method of manufacture. Favorablesurface microtextures may also be present by virtue of bulknon-uniformities' introduced during the manufacturing process. Whencross-sectioned, abraded, or otherwise exposed, these bulknon-uniformities become favorable surface microtextures. Such inherentmicrotextures, present prior to use, may permit the absorption andtransport of slurry particles, thereby providing enhanced polishingactivity without the need to further add micro- or macrotextures.

[0010] There are, however, several deficiencies in polishing padmaterials selected or produced according to the above-describedempirical techniques. Pads made of layers of polymer material may havethermal insulating properties, and therefore unable conduct heat awayfrom the polishing surface, resulting in undesirable heating duringpolishing. Numerous virgin homogenous sheets of polymers such aspolyurethane, polycarbonate, nylon, polyureas, felt, or polyester, havepoor inherent polishing ability, and hence not used as polishing pads.In certain instances, mechanical or chemical texturing may transformthese materials, thereby rendering them useful in polishing.

[0011] However, polyurethane based pads, currently in widespread use,are decomposed by the chemically aggressive processing slurries byvirtue of the inherent chemical nature of urethane. This decompositionproduces a surface modification in and of itself in the case of thepolyurethane pads.

[0012] Yet another approach involves modifying the surface of CMPpolishing pads materials to improve the wetability of the pad surface,the adhesion of surface coatings, and the application performance ofthese materials. Plasma treatment of polishing pad materials is onemeans to functionalize and thereby modify polishing pad surfaces.However, the simple functionalization of pad surfaces by plasmatreatment is known to be a temporary effect, with spontaneous loss offunctionalization after one to two days. While some success in thepreservation of functionalized pad surfaces has been obtained forfluorinated polymeric surfaces, this has not been demonstrated for otherpolymeric surfaces, and in particular, thermoplastics.

[0013] Accordingly, what is needed in the art is an improved process forfunctionalizing and preserving a semiconductor wafer thermoplasticpolishing pad surface, thereby providing a rapid rate of polishing andyet reducing scratches and resultant yield loss duringchemical/mechanical planarization.

SUMMARY OF THE INVENTION

[0014] To address the deficiencies of the prior art, the presentinvention, in one embodiment, provides a polymer, preferablythermoplastic foam polymer, comprising a thermoplastic foam substratehaving a modified surface thereon and a grafted surface on the modifiedsurface.

[0015] In another embodiment, the present invention provides a methodfor preparing a polymer, preferably a thermoplastic foam polymer. Themethod comprises the steps of providing a thermoplastic foam substrate,exposing the substrate to an initial plasma reactant to produce amodified surface thereon, and exposing the modified surface to asecondary plasma reactant to create a grafted surface on the modifiedsurface.

[0016] Yet another embodiment provides a method of manufacturing apolishing pad. The method comprises providing a thermoplastic foamsubstrate, and then forming a thermoplastic foam polishing body with agrafted surface by including those steps described above. A polishingpad is then formed from the thermoplastic foam polishing body that issuitable for polishing a semiconductor wafer or integrated circuit usingthe grafted surface.

[0017] In still another embodiment, the present invention provides apolishing apparatus. This particular embodiment includes a mechanicallydriven carrier head, a polishing platen, and a polishing pad attached tothe polishing platen. The carrier head is positionable against thepolishing platen to impart a polishing force against the polishingplaten. The polishing pad includes a polishing body comprising amaterial wherein the material is a thermoplastic foam polymer.

[0018] The foregoing has outlined, rather broadly, preferred andalternative features of the present invention so that those skilled inthe art may better understand the detailed description of the inventionthat follows. Additional features of the invention will be describedhereinafter that form the subject of the claims of the invention. Thoseskilled in the art should appreciate that they can readily use thedisclosed conception and specific embodiment as a basis for designing ormodifying other structures for carrying out the same purposes of thepresent invention. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention in its broadest form.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For a more complete understanding of the invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawing, in which:

[0020]FIG. 1 illustrates a polishing apparatus, including a polishingpad fabricated using a thermoplastic foam polymer made according to thepresent invention.

DETAILED DESCRIPTION

[0021] Conditions have been discovered for producing a polymer,preferably thermoplastic foam polymer, having desirable polishingproperties. The thermoplastic foam polymer, for example, comprises athermoplastic foam substrate having a modified surface and a graftedsurface on the modified surface. This polymer is produced, for example,by subjecting a thermoplastic foam substrate to a first plasma treatmentto produce a modified surface, thereby allowing the grafting of variousfunctional groups onto the substrate's modified surface in a secondplasma treatment. Such treatments are facilitated using inert gasplasmas such Helium, Neon or Argon. The thermoplastic foam polymers ofthe present invention may also be produced using more reactive plasmagases, such as oxygen. In certain embodiments, the functional effects ofgrafting decline over a period of three to twenty days, as determined bywater contact angle measurements, while in other embodiments thesefunctional effects are preserved. The polymers of the present inventionare ideally suited for use as pads in CMP applications.

[0022] It is believed that exposing polymers, such as thermoplastic foamsubstrates, to an initial plasma reactant creates ruptured single bonds,existing on the polymer surface regime as excited states. Due to the lowmobility and limited vibrational degrees of freedom within the polymermatrix, these triplet sites lack the ability to undergo intersystemcrossing and return to ground state for short periods of time. Based onthe ability of the plasma surface to show large macro effects, excitedstate sites are likely present in abundance at the modified surface.

[0023] The excited state sites generated by exposing polymers, such asthermoplastic foam polymers, to the initial plasma reactant are thoughtto provide an attractive base on which to selectively graft polymerizednumerous inorganic and organic materials. The modified surface of thepolymer incorporating such functional groups is designated as a graftedsurface. Such grafted surfaces are particularly useful in CMP processesdue to the grafting process's ability to introduce very fine hard groupsonto the grafted surface, which is then incorporated into a polishingpad. Such pads may enable the use of reduced or no abrasive slurries,which may improve thermal management. Additionally, the grafting processproduces thermoplastic foam polymers with certain desirable physical andchemical properties, such as controlled wetability surfaces, and renderssuch grafted surfaces permanent. Still other thermoplastic foam polymersmay contain grafted functional groups that change the nanoscalemorphology of a pad surface, while leaving the bulk properties of thethermoplastic polymer relatively intact.

[0024] As noted above, polymers, such as thermoplastic polymers areproduced according to the present invention by a process whereby athermoplastic foam substrate is exposed to primary and secondary plasmamixtures introduced into a conventional plasma generating apparatus. Incertain embodiments, the thermoplastic foam substrate is preferablycomposed of polyurethane, polyolefin or polyvinyl esters. Alternativeembodiments of the thermoplastic foam substrate may be, for example,polyurea, polycarbonate, aliphatic polyketone, polysulfone, aromaticpolyketone, 6,6 nylon, 6,12 nylon or polyamide. In other preferredembodiments, the substrate may be thermoplastic rubber ormelt-processible rubber. However embodiments where the substrate iscomposed of closed-cell polypropylene, polyethylene, crosslinkedpolyethylene, ethylene vinyl acetate, or polyvinylacetate are alsowithin the scope of the present invention.

[0025] One skilled in the art will be familiar with reagents suitablefor producing conventional primary plasma mixtures. For instance,conventional mixtures often include noble gases such as Helium, Neon orArgon; or ammonia, oxygen, or water. In the present invention, theplasma treatment is continued in the presence of a secondary plasmamixture to graft various functional groups onto the polymer surface,depending on the secondary plasma reactant used.

[0026] One group of such secondary plasma reactants areoxygen-containing organometallic reactants that produce a graftedsurface that includes an inorganic metal oxide. In such embodiments, thesecondary plasma mixture typically includes a transition metal such astitanium, manganese, or tantalum. However, any metal element capable offorming an oxygen containing organometallic compound and capable ofbeing grafted to the polymer surface is suitable. Silicon may also beemployed as the metal portion of the organometallic secondary plasmamixture. In these embodiments, the organic portion of the organometallicreagent may be an ester, acetate, or alkoxy fragment. The secondaryplasma reagent may optionally include ozone, alkoxy silanes, water,ammonia, alcohols, mineral sprits or hydrogen peroxide. For example, inpreferred embodiments, the secondary plasma reactant may be composed oftitanium esters, tantalum alkoxides, including tantalum alkoxideswherein the alkoxide portion has 1-5 carbon atoms; manganese acetatesolution in water; manganese alkoxide dissolved in mineral spirits;manganese acetate; manganese acetylacetonate; aluminum alkoxides; alkoxyaluminates; zirconium alkoxides, wherein the alkoxide has 1-5 carbonatoms; alkoxy zirconates; magnesium acetate; and magnesiumacetylacetonate. Other embodiments are also contemplated for thesecondary plasma reactant, for example, alkoxy silanes and ozone, alkoxysilanes and ammonia, titanium esters and water, titanium esters andalcohols, or titanium esters and ozone.

[0027] Another group of secondary plasma reactants produce graftedsurfaces having super hydrated, controlled wetability, and designedalkalinity surface properties. For example, in preferred embodiments,the secondary plasma reactant may be composed of water, aliphaticalcohols, or aliphatic polyalcohols. In other embodiments, the secondaryplasma reactant may be hydrogen peroxide, ammonia, or oxides ofnitrogen. Yet other embodiment include hydroxylamine solution,hydrazine, sulfur hexafluoride as the secondary plasma reactant. Oneskilled in the art, however, will recognize that other similarmaterials, including other organic alcohols or polyalcohols, may producethese desired surface properties when grafted onto the polymer'ssurface, and thus, art within the scope of the present invention.

[0028] Yet another group of secondary plasma reactants result in organicgrafted surfaces. For example, in preferred embodiments, the secondaryplasma reactant may be composed of allyl alcohols; allyl amines; allylalkylamines, where the alkyl groups contain 1-8 carbon atoms; allylethers; secondary amines, where the alkyl groups contain 1-8 carbon;alkyl hydrazines, where the alkyl groups contain 1-8 carbon atoms;acrylic acid; methacrylic acid; acrylic acid esters containing 1-8carbon atoms; methacrylic esters containing 1-8 carbon atoms; or vinylpyridine, and vinyl esters, for example, vinyl acetate.

[0029] The conditions of plasma treatment via Radio Frequency GlowDischarge (RFGD) must be carefully chosen to avoid damaging the graftedlayer, and to achieve long-lasting grafts. For example, high powerplasmas may cause polymer surfaces to crack. See e.g., Owen, M. J. &Smith, P. J. in POLYMER SURFACE MODIFICATION: RELEVANCE TO ADHESION,3-15 (K. L. Mittal, ed., 1995), incorporated herein by reference as ifreproduced herein in its entirety. As further illustrated in experimentsdescribed below, the exact grafting conditions depend on factorsincluding the type of polymer specimen, radio frequency and power, andthe identity of the primary and secondary plasma reactants. However,typical preferred plasma-grafting process conditions include exposingthe thermoplastic foam substrate to a primary plasma reactant treatmenttime (TT-1) from about 30 s to about 30 min, in a reaction chamberhaving a pressure ranging from about 130 to about 340 mTorr, and plasmaback pressure (PBP) ranging from about 140 to about 200 mTorr.Subsequent exposure of the modified substrate surface to the secondaryplasma reactant for similar treatment times (TT-2) and pressures alsoinclude a diluting inert gas, where the inert gas to secondary plasmareactant ratio typically ranges from about 1:1 to about 3:1, thedilutant inert gas being introduced into the reaction chamber at a flowrate of about 0.03 to about 1.0 standard liters per min (SLM). Theamount of secondary reactant monomer in the gas stream is governed bythe monomer vapor pressure (MBP), and the monomer reservoir temperature(MRT), typically ranging from about 20 to about 75° C. The resultingpressure in the reaction chamber during grafting (GP) may range fromabout 135 to about 340 mTorr, and out gas back pressure (OGBP) may rangefrom about 55 to 70 mTorr. Throughout, the RDGD electrode may bemaintained at a constant value within the range of room temperature toabout 100° C. One of ordinary skill in the art understands thatconditions outside of the above-cited ranges may also be used to producethe subject matter of the present invention.

[0030] Polishing pads in certain embodiments of the present inventionmay be manufactured by first melting a thermoplastic polymer pellets inan extrusion apparatus such as a melt extruder, and blowing gas into themelt to form a thermoplastic foam substrate. The substrate may be formedinto pads by techniques well known to those skilled in the art, such aslaser cutting or die cutting. The substrate is next formed into athermoplastic foam polishing body by first exposing the substrate to aninitial plasma reactant to produce a modified surface and then exposingthe modified surface to a secondary plasma reactant to create a graftedsurface on the modified surface. Finally, the polishing body may beincorporated into a pad such that the grafted surface is suitabilitysituated to polish a semiconductor wafer or integrated circuit.

[0031] Polishing pads may be employed in a variety of CMP polishingapparatus 150, one embodiment of which is displayed in FIG. 1. Thethermoplastic foam polymers of the present invention may be incorporatedinto a polishing body 100 that includes a base pad 110, where athermoplastic foam polymer 120 forms a polishing surface located overthe base pad 110. Optionally, a first adhesive material 130, such asacrylate-based, silicone-based, epoxy or other materials well known tothose skilled in the art, may be used to couple the base pad 110 to thethermoplastic foam polymers 120. The polishing pads thus formed may alsohave a second adhesive material 140, well known to those skilled in theart, applied to the platen side. The polishing pad may then be cleanedand packaged for use.

[0032] With continuing reference to FIG. 1, the polishing body 100 maythen be employed in a variety of CMP processes by incorporation into apolishing apparatus 150. The polishing apparatus 150 typically includesa conventional mechanically driven carrier head 160, a conventionalcarrier ring 170, a conventional polishing platen 180, and a polishingpad that includes the polishing body 100 comprising the thermoplasticfoam polymer 120 of the present invention, attached to the polishingplaten 180, optionally using the second adhesive 140. The substrate tobe polished 185, typically a wafer, may be attached to the carrier ringwith the aid of a third a conventional adhesive 190. The carrier head160 is then positioned against the polishing platen 180 to impart apolishing force against the polishing platen 180, typically arepetitive, regular motion of the mechanically driven carrier head 160,while providing an appropriate conventional slurry mixture. Optionally,in certain embodiments of the thermoplastic foam polymer 120, the slurrymay be omitted.

[0033] With continuing reference to FIG. 1, in such polishing processes,a substrate 185 may be polished by positioning the substrate 185, havingat least one layer, on to the above-described polishing apparatus 150,and polishing the layer against the thermoplastic foam polymer 120 ofthe present invention. In one embodiment, the substrate 185 has at leastone layer of material that is a metal layer. In particular embodiments,the metal layer may be is copper or tungsten. In another embodiment, thesubstrate 185 may be a silicon, polysilicon or dielectric materiallocated on a semiconductor wafer. Thermoplastic foam polymers 120 of thepresent invention are particularly suited for polishing in shallowtrench isolation (STI), interlevel dielectrics, and metal interconnectsin integrated circuit fabrication or other fabrication techniques wherelarge areas of field oxide, other dielectrics or metal must be removedfrom the wafer to produce a planar surface prior to subsequentprocessing. The thermoplastic foam polymers 120 of the present inventionare also desirable for polishing metalization materials such as W, Ti,Cu, Al, and other metals as well as nitrides or barrier materials suchas Si₃N₄, TaN, TiN.

EXPERIMENTS

[0034] Measurements of solvent contact angles provides a particularlyuseful means to measure to extent and stability of grafts providingcontrolled wetability surfaces. Wetability, typically measured bymeasuring the contact angle of a water droplet, provides an indicationof surface energy. A hydrophilic surface having a high surface energywill have a low contact angle. Thermoplastic foam polymers madeaccording to the present invention were examined for changes in watercontact angle, by comparing pre- and post-plasma treatment angles,typically for several days following plasma treatment, using commercialinstruments (Rame-Hart Goniometer, Mountain Lakes, N.J.; andAccu-Dyne-Test Marker Pen, Diversified Enterprises, Claremont, N.H.).

[0035] Several such experiments were performed using approximately 2″ by2″ sheets of 0.125″ thick thermoplastic elastomer foam (Santoprene®D-40; Advanced Elastomer Systems, LP, Akron, Ohio). The Santoprene® D-40sheets were manually cleaned with an aqueous/isopropyl alcohol solution,and then placed in the reaction chamber of a conventional commercialRFGD plasma reactor having a temperature controlled electrodeconfiguration (Model PE-2; Advanced Energy Systems, Medford, N.Y.).

[0036] In one experiment, for comparison purposes, plasma treatmentconsisted of exposing the Santoprene® D-40 substrate to only a primaryplasma reactant, comprising Helium:Oxygen, 60:40, for 10 minutes, withthe reaction chamber maintained at 230 mTorr pressure, the electrodetemperature maintained below about 100° C. and using a RF operatingpower of 2500 Watts. Surface modification was confirmed by theobservation of an increased hydrogen and oxygen content to a depth of100 Angstroms, as measured by Electron Spectroscopy Chemical Analysis(ESCA).

[0037] While the pre-treatment water contact angle of the Santoprene®D-40 substrate was 98°, the immediate post-treatment angle was 25°. Thecontact angle, however, subsequently rose to and stabilized at 60° by 6days after treatment. Similar results were obtained in a secondexperiment, when the Santoprene® D-40 substrate was exposed to a primaryplasma reactant of 100% ammonia. The water contact angle was 40°immediately following plasma treatment, but progressively rose to andstabilized at 80° by 6 days post-treatment.

[0038] In a third experiment, the plasma treatment of the Santoprene®D-40 substrate was commenced by introducing the primary plasma reactant,Argon, for 30 seconds within the reaction chamber maintained at 350mTorr. The electrode temperature was maintained at 30° C., and an RFoperating power of 300 Watts was used. Subsequently, the secondaryreactant was introduced for either 10 or 30 minutes at 0.10 SLM andconsisted of either Tetraethoxy Silane (TEOS), Titanium Alkoxide(TYZOR), Allyl-Alcohol (Allyl-OH), or Allyl-Amine (ALLYL-NH₂)vapor mixedwith He or Ar gas (TABLE 1). In this, and analogous experimentsdescribed below, the amount of secondary reactant in the gas stream wasgoverned by the vapor back pressure (BP) of the secondary reactantmonomer at the monomer reservoir temperature (MRT; 50±10° C.). Themonomer-carrier gas mixture was further diluted with a separate streamof either argon or helium in the reactor chamber. The pre-andpost-plasma treatment water contact angles, shown in TABLE 1, revealsubstantially lower immediate post-treatment contact angles as comparedto previously described Santoprene® D-40 substrates treated with theprimary plasma reactant only. TABLE 1 Immediate Seven Day Pre- Post-Post- Secondary Treatment Treatment Treatment Plasma Contact ContactContact Reactant TT-2 (min) Angle (°) Angle (°) Angle (°) TYZOR 10 98 036 TYZOR 30 98 0 65 TEOS 30 98 0 90 Allyl-OH 30 98 0 90 Allyl-NH₂ 30 9865 75

[0039] Similar results were obtained in a fourth experiment, whereSantoprene® D-40 was exposed to a primary plasma reactant of Argonmixture for 30 second at 100 mTorr and 50 Watts RF power, with theelectrode maintained at 40° C., and was exposed to a secondary plasmareactant of 100% ammonia. The pre-treatment water contact angle of 98°was reduced to 40° immediately following treatment, with the angleincreasing to and stabilizing at 60° by 6 days post-treatment.

[0040] In a fifth experiment using Santoprene® D-40 as the substrate,plasma treatment was commenced by introducing the primary plasmareactant, Helium, for 10 minutes with the reaction chamber maintained at350 mTorr pressure, the electrode temperature below about 100° C. and RFoperating power of 3500 Watts was used. This was followed by a second 10minute plasma treatment under the same conditions while introducing asecondary plasma reactant containing tetraethoxyorthosilicate at 0.10SLM into the gas stream. The immediate post-treated surface modifiedthermoplastic foam substrate had a water contact angle of 0°, ascompared to 92° for the pre-treated substrate.

[0041] In a sixth experiment, 1 inch by 1 inch sheets of 0.063 inchthick cross-linked polypropylene foam (type TPR, from Merryweather FoamsInc., Anthony, N. Mex.) was plasma treated under the same conditions asdescribed for Experiment 5. The immediate post-treated surface modifiedthermoplastic foam substrate had a water contact angle of 0°, ascompared to 90° for the pre-treated substrate.

[0042] By careful manipulation of the plasma treatment conditions, thegrafts can be preserved for longer periods, as indicated by thestability of water contact angle changes. This is illustrated by aseventh series of experiments conducted on the above-describedpolypropylene sheets having dimensions of 6 inch by 6 inch by 0.125 inchthickness, under the plasma treatment conditions presented in Table 2.Cold BP (Cold Back Pressure) is measured with the RF power off, whilePBP (Power Back Pressure) is with the RF power on. In experiments 12 and13, PBP was not recorded (n.r.). TABLE 2 Ar dilutant Flow Cold GraftingSample TT-1 OGBP Rate BP PBP GP MRT RF Power Number (min) (mTorr) (SLM)(mTorr) (mTorr) (mTorr) (° C.) (Watts) 1 1 60 0.03 120 140 200 50 50 2 160 0.03 120 140 300 50 50 3 1 65 0.10 190 207 280 70 50 4 1 65 0.03 120150 250 50 100 5 1 70 0.03 125 160 320 50 100 6 1 70 0.03 125 160 200 55100 7 1 60 0.10 180 200 245 50 100 8 1 60 0.10 180 200 340 55 100 9 1 600.03 105 125 150 60 50 10 1 55 0.03 105 125 220 50 50 11 1 60 0.01 90105 130 75 50 12 0 55 0.03 110 n.r. 135 21 50 13 1 55 0.03 110 n.r. 16560 50

[0043] As shown in Table 3, post-treated substrates produced under theconditions described in Table 2 retained their low water contact anglesfor at least 10 days of exposure to laboratory atmospheric conditions.TABLE 3 Sample Pre-treatment Post-treatment Contact Angle (°) NumberContact Angle (°) 0 days 3 days 7 days 10 days 1 90 45 47 50 50 2 90 5865 67 65 3 90 80 73 73 76 4 90 30 42 45 45 5 90 80 75 75 77 6 90 70 7373 76 7 90 70 80 75 76 8 90 68 70 75 76 9 90 75 77 77 75 10 90 75 77 7776 11 90 48 52 59 62 12 90 70 77 75 65 13 90 73 78 75 80

[0044] In an eighth experiment, the polishing efficiency of a padmanufactured according to this invention was compared to a conventionalpolishing pad. A polishing pad was prepared by exposing Aliplast® (JMSPlastic Supplies, Neptune, N.J.; Type 6A: medium foam density andhardness 34 Shore A), a thermoplastic heat moldable cross-linkedpolyethylene closed-cell foam, to the above-described grafting process.Specifically, secondary plasma reactants, containing eitherAllyl-Alcohol, or Allyl-Amine, Tetraethoxy Silane (TEOS), ortetraisopropyl-titanate (TYZOR TPT) monomers, were grafted onto themodified Aliplast® substrate, under conditions similar to Sample number4 shown in Table 1, to produce pads designated as A32AA, A32AN, A32S,and A32T, respectively. The blanket Copper (Cu) polishing properties ofpads fashioned from these polymers were compared to the untreatedAliplast® substrate (designated A32), and to a commercially availableIC1000/SUBA IV pad stack (Rodel, Phoenix, Ariz.).

[0045] The comparison was performed using an CETR CMP simulator (CenterFor Tribology, Inc., Campbell, Calif. Conditions for thermal oxidepolishing include using a down force of 3 psi; table speeds of 0.8m/min; and a conventional slurry comprising K1501 and polishing time of5 min. Conditions for copper polishing include using a down force of 3psi; table speeds of 0.8 m/min; and a conventional slurry comprisingCabot EP-5001 containing 3% hydrogen peroxide and adjusted to a pH ofabout 4, and polishing time of 5 min. Plasma EnhancedTetraethylorthosilicate (PE-TEOS) 5,000 Å wafers having a deposited20,000 Å copper surface and an underlying 250 Å thick tantalum barrierlayer were used for test polishing.

[0046] Cu removal rates for the A32AA, A32AN and A32T pads were about10,000; 7,500; and 7,200 Å/min, respectively. The corresponding Taremoval rates were only 216, 215 and 175 Å/min, respectively. Incomparison, the untreated A32 pad removed Cu at a rate of about 3,200Å/min. The high selectivity of the grafted Aliplast® pads for Cupolishing compared to Tantalum (Ta) polishing may be expressed by theratio of Cu to Ta removal rates. For the A32AA, A32AN and A32T pads, theselectivity ratio was about 46, 35 and 41, respectively. In comparison,the Cu and Ta removal rates of an IC1000/SUBA IV pad stack were about5,700 Å/min and about 170 Å/min, respectively, giving a Cu:Taselectivity of about 34.

[0047] Although the present invention has been described in detail,those skilled in the art should understand that they can make variouschanges, substitutions and alterations herein without, departing fromthe spirit and scope of the invention in its broadest form.

What is claimed is:
 1. A polymer comprising: a thermoplastic foamsubstrate having a modified surface thereon; and a grafted surface onsaid modified surface.
 2. The polymer as recited in claim 1 wherein saidthermoplastic foam substrate is selected from the group consisting of:polyurethane; polyolefin; and polyvinyl esters.
 3. The polymer asrecited in claim 1 wherein said thermoplastic foam substrate is selectedfrom the group consisting of: polyurea; polycarbonate; aliphaticpolyketone; polysulfone; aromatic polyketone; 6,6 nylon; 6,12 nylon; andpolyamide.
 4. The polymer as recited in claim 1 wherein saidthermoplastic foam substrate is selected from the group consisting of:thermoplastic rubber; and melt-processible rubber.
 5. The polymer asrecited in claim 1 wherein said thermoplastic foam substrate is selectedfrom the group consisting of: polypropylene; polyethylene; crosslinkedpolyethylene; ethylene vinyl acetate; and polyvinylacetate.
 6. Thepolymer as recited in claim 1 wherein said modified surface is modifiedby a primary plasma reactant selected from a group of inert gas plasmasconsisting of: Helium; Neon; and Argon.
 7. The polymer as recited inclaim 1 wherein said grafted surface includes an inorganic metal oxidesurface.
 8. The polymer as recited in claim 7 wherein said inorganicmetal oxide surface is created by exposure to a secondary plasmareactant selected from a group of reactive agents consisting of:titanium esters; tantalum alkoxides; manganese acetate; manganesealkoxide; manganese acetate; manganese acetylacetonate aluminumalkoxides; alkoxy aluminates; zirconium alkoxides; alkoxy zirconates;magnesium acetate; and magnesium acetylacetonate.
 9. The polymer asrecited in claim 7 wherein said inorganic metal oxide surface is createdby exposure to a secondary plasma reactant selected from a group ofreactive agents consisting of: titanium esters plus water; titaniumesters plus alcohols; titanium esters plus ozone; alkoxy silanes plusozone; and alkoxy silanes plus ammonia.
 10. The polymer as recited inclaim 1 wherein said grafted surface includes a controlled wetabilitysurface.
 11. The polymer as recited in claim 10 wherein said controlledwetability surface is created by exposure to a secondary plasma reactantselected from a group of reactive agents consisting of: water; aliphaticalcohols; and aliphatic polyalcohols.
 12. The polymer as recited inclaim 10 wherein said controlled wetability surface is created byexposure to a secondary plasma reactant selected from a group ofreactive agents consisting of: hydrogen peroxide; ammonia; and oxides ofnitrogen.
 13. The polymer as recited in claim 10 wherein said controlledwetability surface is created by exposure to a secondary plasma reactantselected from a group of reactive agents consisting of: hydroxylaminesolution; and sulfur hexafluoride.
 14. The polymer as recited in claim 1wherein said grafted surface on said thermoplastic foam substrateincludes an organic grafted surface.
 15. The polymer as recited in claim14 wherein said organic grafted surface is created by exposure to asecondary plasma reactant selected from a group of reactive agentsconsisting of: allyl alcohols; allyl amines; allyl alkylamines, wherethe alkyl groups contain 1-8 carbon atoms; allyl ethers; secondaryamines, where the alkyl groups contain 1-8 carbon atoms; alkylhydrazines, where the alkyl groups contain 1-8 carbon atoms; acrylicacid; methacrylic acid; acrylic acid esters containing 1-8 carbon;methacrylic esters containing 1-8 carbon; vinyl pyridine; vinyl esters.16. A method for preparing a polymer comprising the steps of: providinga thermoplastic foam substrate; exposing said substrate to an initialplasma reactant to produce a modified surface thereon; and exposing saidmodified surface to a secondary plasma reactant to create a graftedsurface on said modified surface.
 17. The method for preparing thepolymer as recited in claim 16 wherein said substrate is selected fromthe group consisting of: polyurethane; polyolefin; and polyvinyl esters.18. The method for preparing the polymer as recited in claim 16 whereinsaid substrate is selected from the group consisting of: polyurea;polycarbonate; aliphatic polyketone; polysulfone; aromatic polyketone;6,6 nylon; 6,12 nylon; and polyamide.
 19. The method for preparing thepolymer as recited in claim 16 wherein said substrate is selected fromthe group consisting of: thermoplastic rubber; and melt-processiblerubber.
 20. The method for preparing the polymer as recited in claim 16wherein said substrate is selected from the group consisting of:polypropylene; polyethylene; crosslinked polyethylene; ethylene vinylacetate; and polyvinylacetate.
 21. The method for preparing the polymeras recited in claim 16 wherein said primary plasma reactant is selectedfrom the group of inert gas plasmas consisting of: Helium; Neon; andArgon.
 22. The method for preparing the polymer as recited in claim 16wherein said grafted surface includes an inorganic metal oxide surface.23. The method for preparing the polymer as recited in claim 22 whereinsaid inorganic metal oxide surface is created by exposure of saidmodified surface to said secondary plasma reactant selected from thegroup of reactive agents consisting of: titanium esters; tantalumalkoxides; manganese acetate; manganese alkoxide; manganese acetate;manganese acetylacetonate aluminum alkoxides; alkoxy aluminates;zirconium alkoxides; alkoxy zirconates; magnesium acetate; and magnesiumacetylacetonate.
 24. The method for preparing the polymer as recited inclaim 22 wherein said inorganic metal oxide surface is created byexposure of said modified surface to said secondary plasma reactantselected from the group of reactive agents consisting of: titaniumesters plus water; titanium esters plus alcohols; titanium esters plusozone; alkoxy silanes plus ozone; and alkoxy silanes plus ammonia. 25.The method for preparing the polymer as recited in claim 16 wherein saidgrafted surface includes a controlled wetability surface.
 26. The methodfor preparing the polymer as recited in claim 25 wherein said controlledwetability surface is created by exposure of said modified surface tosaid secondary plasma reactant selected from the group of reactiveagents consisting of: water; aliphatic alcohols; and aliphaticpolyalcohols.
 27. The method for preparing the polymer as recited inclaim 25 wherein said controlled wetability surface is created byexposure of said modified surface to said secondary plasma reactantselected from the group of reactive agents consisting of: hydrogenperoxide; ammonia; and oxides of nitrogen.
 28. The method for preparingthe polymer as recited in claim 25 wherein said controlled wetabilitysurface is created by exposure of said modified surface to saidsecondary plasma reactant selected from the group of reactive agentsconsisting of: hydroxylamine solution; and sulfur hexafluoride.
 29. Themethod for preparing the polymer as recited in claim 16 wherein saidgrafted surface includes an organic surface.
 30. The method forpreparing the polymer as recited in claim 29 wherein said organicgrafted surface is created by exposure of said modified surface to saidsecondary plasma reactant selected from the group of reactive agentsconsisting of: allyl alcohols; allyl amines; allyl alkylamines, wherethe alkyl groups contain 1-8 carbon atoms; allyl ethers; secondaryamines, where the alkyl groups contain 1-8 carbon atoms; alkylhydrazines, where the alkyl groups contain 1-8 carbon atoms; acrylicacid; methacrylic acid; acrylic acid esters containing 1-8 carbon;methacrylic esters containing 1-8 carbon; vinyl pyridine; vinyl esters.31. A method of manufacturing a polishing pad, comprising: providing athermoplastic foam substrate; forming a thermoplastic foam body by aprocess including: exposing said thermoplastic foam substrate to aninitial plasma reactant to produce a modified surface thereon; andexposing said modified surface on said thermoplastic foam substrate to asecondary plasma reactant to create a grafted surface on said modifiedsurface; and forming a polishing pad from said thermoplastic foam bodysuitable for polishing a semiconductor wafer or integrated circuit usingsaid grafted surface.
 32. The method of manufacturing the polishing padas recited in claim 31 wherein said thermoplastic foam substrate isprovided by extruding a thermoplastic foam substrate from an extrusionapparatus to form said thermoplastic foam substrate.
 33. The method ofmanufacturing the polishing pad as recited in claim 31 wherein saidthermoplastic foam substrate is selected from the group consisting of:polyurethane; polyolefin; and polyvinyl esters.
 34. The method ofmanufacturing the polishing pad as recited in claim 31 wherein saidthermoplastic foam substrate is selected from the group consisting of:polyurea; polycarbonate; aliphatic polyketone; polysulfone; aromaticpolyketone; 6,6 nylon; 6,12 nylon; and polyamide.
 35. The method ofmanufacturing the polishing pad as recited in claim 31 wherein saidthermoplastic foam substrate is selected from the group consisting of:thermoplastic rubber; and melt-processible rubber.
 36. The method ofmanufacturing the polishing pad as recited in claim 31 wherein saidthermoplastic foam substrate is selected from the group consisting of:polypropylene; polyethylene; crosslinked polyethylene; ethylene vinylacetate; and polyvinylacetate.
 37. The method of manufacturing thepolishing pad as recited in claim 31 wherein said primary plasmareactant is selected from the group of inert gas plasmas consisting of:Helium; Neon; and Argon.
 38. The method of manufacturing the polishingpad as recited in claim 31 wherein said grafted surface includes aninorganic metal oxide surface.
 39. The method of manufacturing thepolishing pad recited in claim 38 wherein said inorganic metal oxidesurface is created by exposure of said modified surface to saidsecondary plasma reactant selected from the group of reactive agentsconsisting of: titanium esters; tantalum alkoxides; manganese acetate;manganese alkoxide; manganese acetate; manganese acetylacetonatealuminum alkoxides; alkoxy aluminates; zirconium alkoxides; alkoxyzirconates; magnesium acetate; and magnesium acetylacetonate.
 40. Themethod of manufacturing the polishing pad recited in claim 38 whereinsaid inorganic metal oxide surface is created by exposure of saidmodified surface to said secondary plasma reactant selected from thegroup of reactive agents consisting of: titanium esters plus water;titanium esters plus alcohols; titanium esters plus ozone; alkoxysilanes plus ozone; and alkoxy silanes plus ammonia.
 41. The method ofmanufacturing the polishing pad as recited in claim 38 wherein saidgrafted surface on said thermoplastic foam substrate includes acontrolled wetability surface.
 42. The method of manufacturing thepolishing pad as recited in claim 41 wherein said controlled wetabilitysurface is created by exposure of said modified surface to saidsecondary plasma reactant selected from the group of reactive agentsconsisting of: water; aliphatic alcohols; and aliphatic polyalcohols.43. The method of manufacturing the polishing pad as recited in claim 41wherein said controlled wetability surface is created by exposure ofsaid modified surface to said secondary plasma reactant selected fromthe group of reactive agents consisting of: hydrogen peroxide; ammonia;and oxides of nitrogen.
 44. The method of manufacturing the polishingpad as recited in claim 41 wherein said controlled wetability surface iscreated by exposure of said modified surface to said secondary plasmareactant selected from the group of reactive agents consisting of:hydroxylamine solution; and sulfur hexafluoride.
 45. The method ofmanufacturing the polishing pad as recited in claim 31 wherein saidgrafted surface includes an organic grafted surface.
 46. The method ofmanufacturing the polishing pad as recited in claim 45 wherein saidorganic grafted surface is created by exposure of said modified surfaceto said secondary plasma reactant selected from the group of reactiveagents consisting of: allyl alcohols; allyl amines; allyl alkylamines,where the alkyl groups contain 1-8 carbon atoms; allyl ethers; secondaryamines, where the alkyl groups contain 1-8 carbon atoms; alkylhydrazines, where the alkyl groups contain 1-8 carbon atoms; acrylicacid; methacrylic acid; acrylic acid esters containing 1-8 carbon;methacrylic esters containing 1-8 carbon; vinyl pyridine; vinyl esters.47. A polishing apparatus comprising: a mechanically driven carrierhead; a polishing platen, said carrier head being positionable againstsaid polishing platen to impart a polishing force against said polishingplaten; and a polishing pad attached to said polishing platen andincluding a polishing body comprising a material wherein said materialis a thermoplastic foam substrate having a modified surface thereon; anda grafted surface on said modified surface.
 48. The polishing apparatusas recited in claim 47 wherein said thermoplastic foam substrate isselected from the group consisting of: polyurethane; polyolefin; andpolyvinyl esters.
 49. The polishing apparatus as recited in claim 47wherein said thermoplastic foam substrate is selected from the groupconsisting of: polyurea; polycarbonate; aliphatic polyketone;polysulfone; aromatic polyketone; 6,6 nylon; 6,12 nylon; and polyamide.50. The polishing apparatus as recited in claim 47 wherein saidthermoplastic foam substrate is selected from the group consisting of:thermoplastic rubber; and melt-processible rubber.
 51. The polishingapparatus as recited in claim 47 wherein said thermoplastic foamsubstrate is selected from the group consisting of: polypropylene;polyethylene; crosslinked polyethylene; ethylene vinyl acetate; andpolyvinylacetate.
 52. The polishing apparatus as recited in claim 47wherein said modified surface is modified by a primary plasma reactantselected from a group of inert gas plasmas consisting of: Helium; Neon;and Argon.
 53. The polishing apparatus as recited in claim 47 whereinsaid grafted surface includes an inorganic metal oxide surface.
 54. Thepolishing apparatus as recited in claim 53 wherein said inorganic metaloxide surface is created by exposure to a secondary plasma reactantselected from a group of reactive agents consisting of: titanium esters;tantalum alkoxides; manganese acetate; manganese alkoxide; manganeseacetate; manganese acetylacetonate aluminum alkoxides; alkoxyaluminates;, zirconium alkoxides; alkoxy zirconates; magnesium acetate;and magnesium acetylacetonate.
 55. The polishing apparatus as recited inclaim 53 wherein said inorganic metal oxide surface is created byexposure to a secondary plasma reactant selected from a group ofreactive agents consisting of: titanium esters plus water; titaniumesters plus alcohols; titanium esters plus ozone; alkoxy silanes plusozone; and alkoxy silanes plus ammonia.
 56. The polishing apparatus asrecited in claim 47 wherein said grafted surface includes a controlledwetability surface.
 57. The polishing apparatus as recited in claim 56wherein said controlled wetability surface is created by exposure to asecondary plasma reactant selected from a group of reactive agentsconsisting of: water; aliphatic alcohols; and aliphatic polyalcohols.58. The polishing apparatus as recited in claim 57 wherein saidcontrolled wetability surface is created by exposure to a secondaryplasma reactant selected from a group of reactive agents consisting of:hydrogen peroxide; ammonia; and oxides of nitrogen.
 59. The polishingapparatus as recited in claim 56 wherein said controlled wetabilitysurface is created by exposure to a secondary plasma reactant selectedfrom a group of reactive agents consisting of: hydroxylamine solution;and sulfur hexafluoride.
 60. The polishing apparatus as recited in claim47 wherein said grafted surface on said thermoplastic foam substrateincludes an organic grafted surface.
 61. The polishing apparatus asrecited in claim 60 wherein said organic grafted surface is created byexposure to a secondary plasma reactant selected from a group ofreactive agents consisting of: allyl alcohols; allyl amines; allylalkylamines, where the alkyl groups contain 1-8 carbon atoms; allylethers; secondary amines, where the alkyl groups contain 1-8 carbonatoms; alkyl hydrazines, where the alkyl groups contain 1-8 carbonatoms; acrylic acid; methacrylic acid; acrylic acid esters containing1-8 carbon; methacrylic esters containing 1-8 carbon; vinyl pyridine;vinyl esters.